Why does water have higher entropy than helium?

In summary, the conversation discussed the concept of entropy and why water has a higher entropy than helium under standard conditions. The speaker questioned how a qualitative analysis can lead to this conclusion, as water appears more ordered as a liquid. However, it was mentioned that water has more molecules per volume and those molecules have more freedom in terms of position and orientation, which contributes to its higher entropy. The speaker asked for guidance in understanding this concept.
  • #1
MathewsMD
433
7
Hi,

Under standard conditions, why does water have higher entropy than helium? Isn't helium a gas? I understand that water has more atoms, but it seems more ordered and is a liquid. I'm not sure how a qualitative analysis could lead to the conclusive result that water is higher in entropy compared to helium..

Could anyone please help in guiding me how to properly think about this?
 
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  • #2
Entropy per volume?
Water has much more molecules per volume, and those molecules have more freedom - in addition to the position, they can also vary in their orientations. Water is not ordered.
 

1. Why is water's entropy higher than helium's?

Water has a higher entropy than helium because it has a more complex molecular structure. The molecules in water are larger and have more degrees of freedom, meaning they can move and vibrate in more ways than the smaller and simpler helium molecules. This results in a higher number of microstates, or possible arrangements, for water molecules compared to helium molecules, leading to a higher entropy.

2. How does molecular structure affect entropy?

Molecular structure plays a significant role in determining entropy. In general, substances with more complex and larger molecules tend to have higher entropy because they have more degrees of freedom and can exist in a wider range of arrangements. On the other hand, substances with simpler and smaller molecules, like helium, have lower entropy due to their limited number of possible arrangements.

3. Why is entropy important in understanding the properties of water and helium?

Entropy is an important concept in understanding the properties of substances like water and helium because it helps explain why they behave the way they do. For example, water's high entropy is why it exists as a liquid at room temperature, while helium's low entropy is why it exists as a gas. Additionally, understanding entropy can help predict how substances will react and interact with each other.

4. Can entropy change over time?

Yes, entropy can change over time. In fact, the second law of thermodynamics states that the total entropy of a closed system (a system that does not exchange matter or energy with its surroundings) always increases. This means that as time passes, the entropy of a system will tend to increase, as molecules become more disordered and spread out.

5. Does temperature affect the entropy of water and helium?

Yes, temperature can affect the entropy of water and helium. Generally, as temperature increases, the entropy of a substance also increases. This is because higher temperatures provide more energy for molecules to move and vibrate, increasing the number of possible arrangements they can take on. However, the specific effects of temperature on entropy can vary depending on the substance and its molecular structure.

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